ERC721解读

NFT(非同质化代币):类似于明朝、宋朝的青花瓷。虽然都是青花瓷。但是都具有唯一的典藏价值。而且价值可能不同。 NFT就是具有唯一价值的代币。

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ERC721: 是以太坊规定实现NFT的一种标准了。实现ERC21标准的智能合约就是NFT代币了。

1.接口

1.ERC721

  定义接口参考：ERC 721 - OpenZeppelin 文档

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下面是以太坊官方定义的标准,由于就是我写的代码运行环境不支持payable关键字，因此我打算围绕官方接口定义，按照自己要求稍微增删一下。

pragma solidity ^0.4.25;interface ERC721 {        ///     Event    ///    event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);    event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);    ///     Function    ///    function balanceOf(address _owner) external view returns (uint256); // 返回所有者代币的总个数    function ownerOf(uint256 _tokenId) external view returns (address); // 返回代币id对应所有者的账户地址    // 安全的转账    //  _to:是已经被指定 id 代币的所有者授予的账户 and (接受者不是智能合约 or 接受者实现ERC721Receiver接口的智能合约    // 将给定id的代币转移到接受者账户    // data是元数据，可有可不有(我觉得)    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external;     function safeTransferFrom(address _from, address _to, uint256 _tokenId) external;    // 这个转账对比上述安全转账(少了一个接受者地址实现是否是ERC721Receiver接口的智能合约地址的判断)    function transferFrom(address _from, address _to, uint256 _tokenId) external;    // 授权将代币转移到另一个账户的权限    function approve(address _approved, uint256 _tokenId) external;    // 授权接受者使用所有代币    function setApprovalForAll(address _operator, bool _approved) external;    // 返回授权指定id 代币的接受者账户    function getApproved(uint256 _tokenId) external view returns (address);    // 判断某账户代币的拥有者是否能被某账户全部使用    function isApprovedForAll(address _owner, address _operator) external view returns (bool);}

2.ERC721Metadata

以下就是ERC21的元数据接口，这是可选地。名称、标识符、每一个token对应的tokenURI。

pragma solidity ^0.4.25;interface ERC721Metadata {    function name() external view returns (string);    function symbol() external view returns (string);    function tokenURI(uint256 tokenId) external view returns (string); // 返回指定id的代币所对对应的uri}

3.ERC721Enumerable

另一个额外的可选接口是枚举， 它包含了按索引获取到对应的代币。

pragma solidity ^0.4.25;interface ERC721Enumerable {    // 确定合约当前全部的nft数量(出去销毁)    function totalSupply() external view returns (uint256);    // 从代币列表返回第n个代币    function tokenByIndex(uint256 _index) external view returns (uint256);    // 返回所有者代币列表的第n个代币    function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);}

4.ERC721Receiver

pragma solidity ^0.4.25;// 资产合约interface ERC721Receiver {    function onERC721Received(address operator, address from, uint256 tokenId, bytes data) external        returns (bytes);}

2.实现

1.Jzm721

这是我针对ERC721接口的合约实现。基本满足官方接口标准。

pragma solidity ^0.4.25;import "./ERC721.sol";import "./ERC721Metadata.sol";contract Jzm721 is ERC721,ERC721Metadata {    ///     Filed    ///    string public name;    string public symbol;    uint256  nftCount;    mapping (address => uint[])  balanceMap; // owner => tokenId[]    mapping (uint256=>string)  tokenURIMap; // tokenId => tokenURI    mapping (uint256=>address)  tokenIdMap; // tokenId => owner    mapping (uint256 => address) approveMap; // tokenId => operator(经营方)    mapping (address=>mapping (address=>bool)) approveAllMap; // operator =>(owner => true/false)    ///     Function    ///    constructor(string memory _name,string memory _symbol)     public {        name = _name;        symbol = _symbol;    }    function name() external view returns (string) {        return name;    }    function symbol() external view returns (string) {        return symbol;    }    function tokenURI(uint256 tokenId) external view returns (string) {        return tokenURIMap[tokenId];    }    // 创建代币    function mint(address _owner,string _tokenURI) external  returns (uint256) {        require(_owner != address(0),"owner is not empty address!");        uint256 tokenId = _mint(_owner);        _setTokenURI(tokenId, _tokenURI);        return tokenId;    }    function balanceOf(address _owner) external view returns (uint256) {        return balanceMap[_owner].length;    }    function ownerOf(uint256 _tokenId) external view returns (address) {        return tokenIdMap[_tokenId];    }    // 这里我忽略了data这个元数据的作用    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external {        _transferFrom(_from, _to, _tokenId);        if(_isContractAdd(_to)) {            if(_checkIfFunctionExists(_to)) {                _externalTransfer(_from, _to, _tokenId);                emit Transfer(_from, _to, _tokenId);            }          }    }    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external {        _transferFrom(_from, _to, _tokenId);        if(_isContractAdd(_to)) {            if(_checkIfFunctionExists(_to)) {                _externalTransfer(_from, _to, _tokenId);                emit Transfer(_from, _to, _tokenId);            }        }    }    function transferFrom(address _from, address _to, uint256 _tokenId) external {        _transferFrom(_from, _to, _tokenId);    }    function approve(address _approved, uint256 _tokenId) external {        require(_approved != address(0),"approved is not empty address!");        address owner = msg.sender;        approveMap[_tokenId] = _approved;         emit Approval(owner,_approved,_tokenId);    }    function setApprovalForAll(address _operator, bool _approved) external {        require(_operator != address(0),"operator is not empty address!");        address owner = msg.sender;        approveAllMap[_operator][owner] = _approved;        emit  ApprovalForAll(owner,_operator,_approved);    }    function getApproved(uint256 _tokenId) external view returns (address) {        return _getApproved(_tokenId);    }    function isApprovedForAll(address _owner, address _operator) external view returns (bool) {        return _isApprovedForAll(_owner,_operator);    }    function _checkIfFunctionExists(address _add)public  returns (bool) {        bytes4 functionSelector = bytes4(keccak256("onERC721Received(address,address,uint256,bytes)")); // 函数选择器，基础原型前4个字节        bytes memory data = abi.encodeWithSelector(functionSelector, address(0),address(0),0,"");        bool success = _add.call(data);        return success;    }    function _transferFrom(address _from, address _to, uint256 _tokenId) private {        // from不能是零地址。        require(_from != address(0),"from is not empty address!");        // to不能是零地址。        require(_to != address(0),"from is not empty address!");        // tokenId令牌必须存在并由from拥有。        require(tokenIdMap[_tokenId] == _from,"The tokenId  must exist and be owned by from!");        // 接受者一方不是合约地址        if (!_isContractAdd(_to)) {            if (_isApproved(_from, _to, _tokenId)) {                 // TODO                _externalTransfer(_from, _to, _tokenId);                emit Transfer(_from, _to, _tokenId);            }        }    }    function _externalTransfer(address _from,address _to,uint256 _tokenId) private {        // 删除代币批准        if(_getApproved(_tokenId) == _to) {            approveMap[_tokenId] = address(0);           }        // 转账        _deleteAccountToken(_from,_tokenId);        tokenIdMap[_tokenId] = _to;        balanceMap[_to].push(_tokenId);    }    function _deleteAccountToken(address _owner,uint256 _tokenId) private {        uint256[] storage tokenIds = balanceMap[_owner];        uint len =  tokenIds.length;        for (uint i = 0; i  0;    }    function _getApproved(uint256 _tokenId) private view returns(address) {        return approveMap[_tokenId];    }    function _isApproved(address _owner, address _operator,uint256 _tokenId) private view returns (bool) {        bool approved = _getApproved(_tokenId) == _operator;        return approved || _isApprovedForAll(_owner, _operator);    }    function _isApprovedForAll(address _owner, address _operator) private view returns(bool) {        return approveAllMap[_operator][_owner];    }}

2.Jzm721Receiver

在这里我就是想要满足合约地址的合约实现ERC721Receiver接口的标准。原合约，这里该函数涉及代币的转账，由于环境的原因，不支持payable关键字，我这里是无法满足的。

pragma solidity ^0.4.25;import "./ERC721Receiver.sol";contract Jzm721Receiver is ERC721Receiver {    function onERC721Received(address operator, address from, uint256 tokenId, bytes data) external        returns (bytes) {            return data;        }}